Less durability (no crash-only design) because writes are not immediately synced with the file system. This means that the write performance is higher, but data can get lost after a crash. From version 1.7.5 journalling is supported which provides more durability, but this seems to be work-in-progress.

CouchDB

Main characteristics

JSON format

Erlang

Apache license

MVCC (Multi-Version Concurrency Control), which means that updates always result in new documents with a version+1. This leads to less performance in writes, but contributes to the crash-only design of CouchDB. This approach also enables you to use versioned updates, so you can check if the document still has the same version identifier to check if there was another update.

No adhoc query, so indexes have to be created

General REST interface that can be used for CRUD operations. There are several driver projects which make it easier to use the REST interface.

Only atomic transactions

Master-Master replication, which means that it's very well suited for offline work getting synced to the database server.